Premise of the study: Taxa inhabiting the California Channel Islands exhibit variation in their degree of isolation, but few studies have considered patterns across the entire archipelago. We studied phylogeography of insular Acmispon argophyllus and A. dendroideus to determine whether infraspecific taxa are genetically divergent and to elucidate patterns of diversification across these islands.
Methods: DNA sequences were collected from nuclear (ADH) and plastid genomes (rpL16, ndhA, psbD-trnT) from >450 samples on the Channel Islands and California. We estimated population genetic diversity and structure, phylogenetic patterns among populations, and migration rates, and tested for population growth.
Key results: Populations of northern island A. argophyllus var. niveus are genetically distinct from conspecific populations on southern islands. On the southern islands, A. argophyllus var. argenteus populations on Santa Catalina are phylogenetically distinct from populations of var. argenteus and var. adsurgens on the other southern islands. For A. dendroideus, we found the varieties to be monophyletic. Populations of A. dendroideus var. traskiae on San Clemente are genetically differentiated from other conspecific populations, whereas populations on the northern islands and Santa Catalina show varying degrees of gene flow. Evidence of population growth was found in both species.
Conclusions: Oceanic barriers between islands have had a strong influence on population genetic structure in both Acmispon species, although the species have differing phylogeographic patterns. This study provides a contrasting pattern of dispersal on a near island system that does not follow a strict stepping-stone model, commonly found on isolated island systems.
Keywords: Acmispon argophyllus; Acmispon dendroideus; California Channel Islands; Last Glacial Maximum; dispersal; endemism; phylogeography.
© 2017 Botanical Society of America.